Variable capacitor of the locking type

ABSTRACT

The invention here disclosed is a variably positioned capacitance or susceptance element of particular utility in tuning striplines and cavities excited in the TEM mode. It is characterized by a bushing having an expansible segmented fore portion which projects through an aperture in the wall of the device being tuned, together with a locking screw arranged to force the segments into the edges of said aperture, thereby to assure favorable electrical characteristics and a secure lock of the setting of capacitance or susceptance.

ilnited Statea Patent [72] Inventor Carroll 1E. Weller Cincinnati, Ohio[2]] App]. No. 9,220 [22] Filed Feb. 6, 1970 [45] Patented Nov. 2, 19711[73] Assignee Avco Corporation Cincinnati, Ohio [54] VARIABLE CAPACITOR011* THE LOCKING TYPE 3 Claims, 7 Drawing Figs.

[52] 11.8. CI 333/83 1R, 333/98 R, 151/31, 85/84 [51] Int.Cl111101p7/06, F16b 39/06, F16b 39/284 [50] Field otsearch 333/97,98;151/31; 85/84 [56] References Cited UNITED STATES PATENTS 1,279,9199/1918 Scusa 151/31 Primary Examiner- Herman Karl Saallbach AssistantExaminerwm. H. Punter Attorney-Charles M. Hogan ABSTRACT: The inventionhere disclosed is a variably positioned capacitance or susceptanceelement ofparticular utility in tuning striplines and cavities excitedin the TEM mode. It is characterized by a bushing having an expansiblesegmented fore portion which projects through an aperture in the wall ofthe device being tuned, together with a locking screw arranged to forcethe segments into the edges of said aperture, thereby to assurefavorable electrical characteristics and a secure lock of the setting ofcapacitance or susceptance.

PATENTEU rem/2 I971 .R mE (L TL NE V W WE L L O R R A C ATTORNEY.

VARIAIIIILIE IIAIPA'CI'IGR (IF THE LOCKING TIIIPIE BACKGROUND OF THEINVENTION AND OBJECTS One purpose of the invention is to provide acapacitor hav ing negligible series resistance and parasitic inductance.Correlatively, another object of the invention is to provide a capacitorhaving high values of Q and self-resonant frequency.

A further objective is to accomplish firm and secure mechanical lockingwithout disturbing any one of many possible capacitance or susceptancesettings.

The low loss capacitor in accordance with the invention is useful inultra high frequencies and microwave frequencies. In one form it is usedas a variable susceptance in the tuning of a wave guide.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention,together with other and further objects, advantages and capabilitiesthereof, reference is made to the following description of theaccompanying drawings, in which:

FIG. I is a perspective view of a variably positioned capacitanceelement in accordance with the invention;

FIG. 2 is a sectional view through the end wall ofa coaxial cavityshowing a longitudinal section of the FIG. 1 capacitance element asinstalled in place, and in association with an inductor;

FIG. 3 is an end view of the wave guide wall showing the location ofwrench receiving apertures in the FIG. I capacitor;

FIG. I is a form of wrench suitable for use in adjusting the capacitor;

FIGS. 3 and 6 are longitudinal sectional views of modified forms ofcapacitance element in accordance with the invention;

FIG. 7 is an elevational sectional view of a preferred form of variablesusceptance device in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring first specifically toFIG. 2, there is shown a section of the end wall ofa coaxial cavity II)in which is mounted an inductive element II (pictorially shown). Theinvention is useful in any tunable structure having distributedparameters. The coaxial cavity is tuned to resonance by means ofacylindrical piece of metal which is variably positioned with respect tothe inductive element II. In accordance with the invention, there isprovided a structural tuning means in the form of a variably positionedtuning element I2 which is adapted to be fitted into an aperture in thetunable structure It) and to be variably projected into the resonantstructure so as to tune it. The aperture I3 is circular in form as itopens out into the interior of the cavity. The rear portion of theaperture I3 is enlarged and provided with threads 14.

The variably positioned bushing I2 is hollow and its fore portion ismultiply split as illustrated by slot IE to provide four or more arcuatesegments such as 16 and I7. The rear portion of bushing I2 is enlargedor flanged and is formed with threads 18, complementary to threads Id,so that the bushing may be advanced or retracted into the aperture I3and variably positioned as desired.

It is important that, when the capacitance parameter is predetermined bya selected positioning of the bushing 12, the bushing then be locked inplace in such a manner as not to upset the capacitance parameter of thetuned cavity. For that purpose the bushing I2 is formed interiorly, nearits front, with a' generally conical ball-containing compartment,converging towards the front and providing thrust surfaces I9. Lockingmeans adapted to bear against said thrust surface 19 is provided in thesubcombination of a setscrew 20 and a ball 21, confined within saidconical chamber, said ball being generally the equivalent of a bluntnose on the setscrew in that the ball is advanced against the thrustsurfaces, the ball being seated in a concave seat 22 on the front of thesetscrew.

Referring now to FIG. I, there is shown a wrench, comprising a wafer 23from which project four prongs, such as 26, 23 and 26, adapted to beseated in complementary depressions such as 26, 29 and 30, for example,formed on the rear face of bushing I2. The wafer 23 is manually turnedto advance or retract bushing I2, as required. TI-Ie depressions areshown in FIG. 3.

Referring again to FIG. 2, the bushing is longitudinally threaded asshown at BI and the setscrew is threaded in complementary fashion. Aslot 32, formed in the end of the setscrew permits its adjustment as aconventional screw.

When the coaxial cavity has been tuned to the desired frequency bypositioning bushing I2, setscrew 20 is then ad vanced so as to push ball21 against the thrust surfaces I9, thereby forcing the segments, such asI6 and I7, radially outwardly and into firm positive contact with thesidewalls of the aperture in the cavity. The expansion of the segmentsinto contact with the sidewall is accompanied by negligible change inthe capacitance between the elements II and I2. The positive metalcontact between the segments and sidewalls of the aperture providessolid grounding and reduces the series resistance and the parasiticinductance of the capacitor.

A modified form of variably positioned tuning element is illustrated inFIG. 5. In this form the ball 211 is omitted and the wedging action forcausing the segments of the bushing to expand is provided by forming thenose of the setscrew with a conical surface 33. Additionally, anintegral nut formation 34 is formed at the rear of the bushing toprovide for adjustment ofthe bushing, here numbered I2.

In FIG. 6, there is illustrated still another modified form in which thewedging action is obtained! by shaping the front of the locking screw inblunt-nosed bulletlike fashion, as indicated at 35. The exterior threadsIII of this bushing, extend substantially throughout its length. It willbe understood that this bushing is adapted to be fitted into a threadedaperture of uniform diameter in the wave guide, thus simplifyingmachining operations for forming the aperture. Adjustment of theposition of the FIG. 6 bushing I2" is accomplished by the use ofa nutformation 34'.

Referring now specifically to FIG. 7, the structural tuning means, hereshown, comprises a. generally cylindrical susceptance element 36together with the cooperating bushing element 63. The susceptanceelement 36 has three or more slots, having uniform angular displacement,cut as shown at 611. The slots cut into susceptance element 36 make itcapable of bulging or expansion at its interface with wall It). Thebushing element 43 is formed in accordance with the teaching of theFIGS. 2 and 6 embodiments, having a ball 2I of FIG. 2 and the continuousthreads 18 of the FIG. 6 embodiment. The expression structural tuningmeans" as applied to FIG. 7 includes both the susceptance element 36 andthe bushing 63. The last element is split to provide expansiblesegments, so that both elements have expansible portions.

In the FIG. 7 embodiment, the forward end of the susceptance element 36is projected into the wave guide 10 a significant distance.

The susceptance element 36 is exteriorly threaded as shown at 38 and isformed at its trailing end with an integral nut 62, so that thesusceptance element can be adjustably threaded into the threadedaperture 46 formed in wave guide 16', also into the threads 39 of collar45.

Secured to the exterior of the wave guide It) is the metallic collar I5,formed with screw threads 39 in alignment with screw threads III.

The bushing 43 of FIG. 7 is exteriorly threaded to complement theinterior threads 3'7.

In preparing for operation, the susceptance element 36 is firstpositioned as desired. Then the bushing 43 is advanced so that itprojects slightly into the wave guide. Finally, setscrew 20 is advancedto cause expansion of the fore portions of the bushing 43 and the wallof susceptance element 36 to lock all of the parts in secure position.

When the wave guide is pressurized, a flanged cap 46 is screwed on tocollar 45 and sealing is provided by a suitable gasket 47.

In the FIG. 2 embodiment, the expansible portions of the element 12participate in the performance of the functions of tuning, locking andproviding a secured ground. Similarly, in the embodiment of FIG. 7, theexpansible portions of the susceptance element 36 participate in thefunctions of tuning, grounding and locking.

While there have been shown and described what are presently understoodto be the preferred embodiments of the invention, it will be understoodby those skilled in the art that various changes and modifications maybe made therein without departing from the scope of the invention asdefined in the appended claims.

1. For use in a tunable structure of the type having distributedparameters and formed with a receiving opening having a wall, thecombination of:

structural tuning means adapted to be adjustably projected into saidstructure,

said structural tuning means comprising a variably positionedsusceptance element adapted to be fitted into said opening and a bushingmember adapted to project into said susceptance member,

said susceptance element and said bushing member being split to provideexpansible portions, and

means for forcing said expansible portions outwardly against the wall ofsaid opening to lock said structural tuning means in the desiredposition.

2. The combination in accordance with claim 1 in which the bushing isformed interiorly with thrust surfaces and in which the locking meanswedges against said thrust surfaces.

3. The combination in accordance with claim 2 in which the susceptanceelement is exteriorly threaded adjustably to fit into the tunablestructure,

the bushing is exteriorly threaded adjustably to fit into thesusceptance element and the locking means includes a setscrew exteriorlythreaded to fit into the bushing.

t l l I! t

1. For use in a tunable structure of the type having distributedparameters and formed with a receiving opening having a wall, thecombination of: structural tuning means adapted to be adjustablyprojected into said structure, said structural tuning means comprising avariably positioned susceptance element adapted to be fitted into saidopening and a bushing member adapted to project into said susceptancemember, said susceptance element and said bushing member being split toprovide expansible portions, and means for forcing said expansibleportions outwardly against the wall of said opening to lock saidstructural tuning means in the desired position.
 2. The combination inaccordance with claim 1 in which the bushing is formed interiorly withthrust surfaces and in which the locking means wedges against saidthrust surfaces.
 3. The combination in accordance with claim 2 in whichthe susceptance element is exteriorly threaded adjustably to fit intothe tunable structure, the bushing is exteriorly threaded adjustably tofit into the susceptance element and the locking means includes asetscrew exteriorly threaded to fit into the bushing.